1. Field
This disclosure relates to formation of textured regions on surfaces of materials by ultrashort optical pulses and to formation of images on materials. The disclosure also relates to techniques for optical modulation of ultrafast pulse trains.
2. Description of Related Art
In conventional ink printing, grayscales in images are generally created by using binary pixels of pre-defined size. For example, “on” may correspond to black and “off” may correspond to white. Grayscale may be produced by varying the density of “on” (e.g., black) pixels. As such, white images portions have few or no “on” pixels, black image portions have “on” pixels substantially covering the image portion, while gray image portions have varying densities of “on” pixels to achieve the desired grayscale. Thus, the image contrast is essentially determined by the number of gray levels, which is inherently determined by pixel size.
Pixels can be fabricated by a variety of methods. One method is ink-jet printing, where a jet of ink is deposited at various densities on a substrate. This method works very well for paper substrates but has limited utility for solid substrates such as metals. Generally, imaging techniques can be characterized as comprising the following actions: 1) digitizing an image; 2) creating a surface pattern; and 3) correlating the surface pattern with the digital image. In conventional ink-jet printing, 1) corresponds to calculation of the pixel density based on the grayscale of the image; 2) corresponds to deposition of the ink; and 3) corresponds to the density of ink-pixels on the image.
Lasers can be used to for patterning images on solid substrates. In conventional laser engraved grayscale images, image contrast is generally determined by machining depth. However, conventional laser engraving is very sensitive to laser irradiation parameters.